Re-usable expandable plastic nut for two-piece fastener

Abstract

A two-piece fastener comprises a screw and a plastic nut for releasably securing together two apertured panels. The screw comprises a screw head and a threaded screw shank insertable in the aperture of one panel. The nut comprises a nut head, a nut shank insertable in the aperture of the other panel, and a bore extending through both the nut head and nut shank to receive the screw shank. The nut shank has an expandable portion, a screw-engaging portion, and a common wall therebetween. The bore has an unthreaded bore region through the nut head and through expandable nut shank portion, an intermediate bore region through the common wall and in a part of the screw-engaging nut shank portion, and a threaded bore region through the screw-engaging nut shank portion. The expandable nut shank portion comprises a plurality of thin, flexible, resilient walls, each connected between the common wall and the nut head. Each flexible wall has a parabolically shaped recess on its inner surface along which it can bend. Each adjacent pair of flexible wall is separated by a slit which extends axially from the common wall and through the nut head. A single thread on the wall of the intermediate bore region engages the screw thread to maintain the screw and nut in pre-assembled condition and to guide the screw thread into engagement with discrete screw-engaging thread sections formed in the threaded bore region.

We claim: 
     
       1. A plastic expansion nut for receiving a screw comprising: a nut shank having a head end and an insertion end,   said nut shank comprising an outwardly expandable portion near its head end, and a screw-engaging portion near its insertion end and a common wall joining said portion;   a nut head at said head end of said nut shank;   a screw-receiving bore having a bore wall and extending through said nut head, through said nut shank and through said common wall;   a screw-engaging thread formed on said bore wall of said common wall of said nut shank;   a plurality of discrete screw-engaging thread sections formed on said bore wall of said screw-engaging portion of said nut shank between said screw-engaging thread and said insertion end of said nut shank,   some of said discrete thread sections being located on one side of said bore wall and the others being located on the opposite side of said bore wall, those discrete thread sections on each wall being axially spaced apart from each other;   said nut shank having a plurality of resiliently flexible outwardly expandable wall sections located between said nut head and said screw-engaging thread to define said outwardly expandable portion,   said outwardly expandable nut shank portion having a non-circular cross-sectional configuration,   each wall section having a flat outer surface and a flat inner surface and having a depression of parabolic cross-sectional configurations formed in said flat inner surface thereof to facilitate bending of said wall section,   each said wall section being defined by a pair of slots communicating between the outside of said nut and the bore therewithin,   each slot extending axially along said nut shank and extending through said nut head.   
     
     
       2. A plastic expansion nut according to claim 1 wherein said screw-engaging thread takes the form of a single wrap of thread extending through approximately 360°. 
     
     
       3. A plastic expansion nut according to claim 1 wherein said expandable portion of said nut shank has a rectangular outer cross-sectional configuration and has four of said wall sections. 
     
     
       4. A two-piece fastener comprising a screw and a nut for releasably securing together two components, each of which component has an aperture therethrough; said screw comprising:   a screw shank;   a screw head at one end of said screw shank;   and a screw thread on said screw shank;   said nut comprising:   a nut shank;   a nut head at one end of said nut shank;   and a screw-receiving bore extending through said nut head and said nut shank;   said nut shank having:   an expandable portion,   a screw-engaging portion,   and a common wall between said portions;   said bore having:   an unthreaded region through said nut head and through said expandable portion of said nut shank,   an intermediate region through said common wall and in a part of said screw-engaging portion of said nut shank,   and a threaded region through said screw-engaging portion of said nut shank;   said expandable portion of said nut shank comprising a plurality of flexible wall sections, each wall section having a flat outer surface and a flat inner surface and being connected at one end to said common wall and connected at its other end to said nut head, each wall section being provided on its flat inner surface with a recess of parabolic cross-sectional configurations along which the wall section may bend, each adjacent pair of wall sections being separated by a slot which extends axially from said common wall and through said nut head;   a screw-engaging thread on a bore wall defining said intermediate region of said bore for threadedly engaging said screw thread on said screw to maintain said screw and nut in preassembled condition and to guide said screw thread into said threaded region;   and discrete screw-engaging thread sections on opposite bore walls defining said threaded region.   
     
     
       5. A fastener according to claim 4 wherein said screw-engaging thread takes the form of a single wrap of thread extending through approximately 360°. 
     
     
       6. A fastener according to claims 4 or 7 wherein said expandable portion of said nut shank has a rectangular outer cross-sectional configuration and has four of said wall sections. 
     
     
       7. A plastic expansion nut for receiving a screw comprising: a nut shank having a head end and an insertion end,   said nut shank comprising an outwardly expandable portion near its head end, and a screw-engaging portion near its insertion end and a common wall joining said portion;   a nut head at said head end of said nut shank;   a screw-receiving bore having a bore wall and extending through said nut head, through said nut shank and through said common wall;   a screw-engaging thread formed on said bore wall of said common wall of said nut shank;   a plurality of discrete screw-engaging thread sections formed on said bore wall of said screw-engaging portion of said nut shank between said screw-engaging thread and said insertion end of said nut shank,   some of said discrete thread sections being located on one side of said bore wall and the others being located on the opposite side of said bore wall, those discrete thread sections on each wall being axially spaced apart from each other;   said nut shank having a plurality of resiliently flexible outwardly expandable wall sections located between said nut head and said screw-engaging thread to define said outwardly expandable portion,   said outwardly expandable nut shank portion having a non-circular cross-sectional configuration,   each wall section having a flat inner surface and a flat outer surface and having a depression formed in said flat inner surface thereof, said depression being spaced from said nut head and from said screw-engaging thread to facilitate bending of said wall section intermediately of its opposite ends,   each said wall section being defined by a pair of slots communicating between the outside of said nut and the bore therewithin,   each slot extending axially along said nut shank and extending through said nut head.   
     
     
       8. A plastic expansion nut according to claim 7 wherein said screw-engaging thread takes the form of a single wrap of thread extending through approximately 360°. 
     
     
       9. A plastic expansion nut according to claims 7 or 8 wherein said expandable portion of said nut shank has a rectangular outer cross-sectional configuration and has four of said wall sections.